Such control devices are believed to be generally understood. For example, a control knob, which has an actuating element which is rotatable in relation to a housing, is discussed in EP 0 842 822 A2. Such rotary knobs are used, for example, in car radios and the like. Normally, the actuating element is mechanically coupled to a potentiometer, the rotary position of the rotary knob being converted by the potentiometer into a corresponding electrical signal in order, for example, to set the sound volume of the car radio with the aid of the rotary knob. It is disadvantageous that potentiometers have sliding contacts that wear away over time.